Radioisotopes: Their Uses in Medical Diagnosis and Therapy

Radiation is used to both detect and treat abnormalities in the body. We've already
discussed the use of iodine-131 therapy for hyperthyroidism. Iodine-131 can also be used
in a diagnostic procedure to monitor the function of the thyroid. The rate at which the
thyroid rakes up the iodine-131 can be monitored with a scanning device to see if it is
functioning properly.

What makes radioisotopes so useful in diagnostic procedures is that the body treats the
tagged isotope in the same way that it treats the nonradioactive element. Therefore, the
tagged isotope goes right to the area of the body where you want it to go. For example,
iodine, whether it's radioactive or not, goes right to the thyroid, where it is
incorporated into the amino acid thyroxine (the only molecule in the body that contains
iodine). Therefore, iodine-131 is perfect for monitoring the thyroid gland.

Chromium, in the form of sodium chromate, attaches strongly to the hemoglobin of red
blood cells. This makes radioactive chromium-151 an excellent isotope for determining the
flow of blood through the heart. This isotope is also useful for determining the lifetime
of red blood cells, which can be of great importance in the diagnoses of anemias.

Radioactive cobalt (cobalt-59 or cobalt-60) is used to study defects in vitamin B12
absorption. Cobalt is the metallic atom at the center of the B12 molecule. By
injecting a patient with vitamin B12, labeled with radioactive cobalt, the
physician can study the path of the vitamin through the body and discover any
irregularities.

We've already discussed how radiation therapy can be used to destroy cancer cells.
Radiation can be delivered to a malignant area in three ways.

One method is teletherapy, in which a high-energy beam of radiation is aimed at the
cancerous tissues. A second method is brachytherapy, in which a radioactive isotope is
placed into the area to be treated. This is usually done by means of a seed, which could
be a glass bead containing the isotope. In this way the isotope delivers a constant beam
of radiation to the affected area.

The third method is called radiopharmaceutical therapy. This method involves oral or
intravenous administration of the isotope. The isotope then uses the normal body pathway
to seek its target. This is the method that is used to get iodine-131 to the thyroid
gland.